1. Field of the Invention
The present invention relates to a hydrophilic film for an ex vivo membrane and the ex vivo membrane.
2. Description of the Related Art
Various ex vivo test strips are being actively developed. Those strips use urine, stool, blood, saliva or other bodily fluids as samples for detecting various health indexes or physiological conditions of humans. Improving the stability and accuracy of test strips is a target that manufacturers are continually striving to accomplish. Blood glucose test strips receive the broadest attention. Annual increases in diabetic populations are driving industrial research on improving blood glucose test strips.
Generally, the ex vivo test strip has a structure as shown in FIG. 1, in which a hydrophilic film 11 is combined with a middle barrier layer 12, to form a flow channel 13 which allows a test fluid to enter a detection layer 14. The hydrophilic film 11 is composed of a substrate 111 (which is generally a transparent plastic substrate) and a hydrophilic layer 112.
The structure of the ex vivo test strip is further illustrated in FIG. 2. As shown in FIG. 2, the function of the hydrophilic film 11 is to promote the delivery of the test fluid, whereby the test fluid enters a detection region 15 in the detection layer 14 via the flow channel 13, while the detection region 15 is protected against contamination and isolated from external interference. Also, the hydrophilic film 11 has the function of providing measurement stability. To avoid failure of the ex vivo test strip due to degradation from contact with ambient moisture, oxygen, or UV light, the hydrophilic film 11 is required to have good resistance to humidity and heat, high hydrophilicity, and other properties. Moreover, the volume of the flow channel 13 needs to remain constant, to ensure measurement stability. Therefore, the hydrophilic layer 112 in the hydrophilic film should be firmly adhered to the substrate 111.
The materials of the hydrophilic layer commonly used in the art mainly include hydrophilic resins or surfactants. The surfactants (e.g. a sulfonate compound) have the advantages of good hydrophilicity and a relatively low amount to be used. However, the surfactants are susceptible to environmental conditions causing degradation. Therefore, a hydrophilic resin with good hydrophilicity and wettability and high resistance to humidity and heat may be used in combination with a surfactant as the materials of a hydrophilic layer.
At present, the commercially available hydrophilic film used for medical diagnosis is exemplified by the product 9962 from 3M Inc. The hydrophilic layer of the hydrophilic film includes a polyvinylidene chloride coating comprising an alkylbenzyl sulfonate based surfactant. Although a biological fluid may be delivered by the diagnosis strip made from such a hydrophilic film, the product is shown through testing to have significant defects such as inadequate uniformity, delivery rate and anti-aging stability.
Other commercially available hydrophilic films include ARflow 90128 and ARflow 90469 from Adhesives Research Inc. These products include a polyester film coated with a composition comprising a thermoplastic co-polyester and a surfactant, and having a mode of action similar to the above-mentioned product from the 3M Inc. To avoid non-uniformity, quite a large amount of surfactant (about 5 to 8%) is added, causing the hydrophilic coating to have a waxy surface. Because a sufficient bonding strength cannot be attained when the coating is bound to a pressure sensitive tape, delamination of the assembly frequently occurs during the fabrication of the test strip.
In addition to the above-mentioned defects, the hydrophilic film is required to be patterned during the manufacture of an ex vivo membrane from a conventional hydrophilic film, resulting in frequent failure of the hydrophilic coating due to fouling of the surface of the hydrophilic coating by printing ink or sweaty hands. Therefore, the hydrophilic coating should be shielded or covered with an additional protective layer, making the process troublesome and costly.
Consequently, the inventors provide a novel hydrophilic film for an ex vivo membrane, by which the aforesaid problems are effectively solved. The hydrophilic film according to the present invention has a special hydrophilic coating having a robust bonding strength to the substrate, by which the stripping of the hydrophilic layer occurring during processing can be avoided, and which is beneficial to subsequent processing and manufacturing, thereby simplifying the process steps and reducing cost. Moreover, the present invention has excellent hydrophilicity and resistance to humidity and heat, whereby the ineffectiveness of the ex vivo membrane resulting from degradation and failure of the hydrophilic film due to exposure to adverse environmental conditions can be avoided. Therefore, the shelf life of the ex vivo membrane can be effectively extended by the hydrophilic film of the present invention.